1. Field of the Invention
The present invention relates to the sequential processing of items bearing printed indicia, envelopes having address information printed thereon for example, and particularly to the introduction of an extended time delay in the transport of such items while maintaining physical separation between the sequentially moving items and without discontinuing item movement. More specifically, this invention is directed to apparatus which introduces an extended time delay in the path of a high-speed, linear sequential document transport and especially to a buffer device which intercepts a stream of indicia bearing paper items, changes the direction and velocity of motion thereof and subsequently delivers the items to a downstream high-speed transport without any interruption in the continuous movement of the items and without commingling of the items. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
While not limited thereto in its utility, the present invention is particularly well suited for use in a mail processing system where address information on envelopes is "read" electronically, postal ZIP-Codes corresponding to the addresses are determined and bar codes corresponding to the postal ZIP-Code information are printed on the envelopes. In such a mail processing system, an envelope imaging camera located along a high-speed linear document transport, typically at a point immediately downstream of an envelope feeder, initiates a complex, high-speed, computer-pipelined, queue of linearly-segmented processes that must be completed by the time the envelope reaches a downstream sorter and bar code printer. These processes include capture and recording of an image of the envelope, locating the address information, employing optical character recognition technology to "read" the address and looking-up the 11-digit postal ZIP-Code for the address in a national address directory database. These process steps must be performed while attempting to manage and recover from various "normal" error conditions. The "answer" derived from these processes for a specific envelope must be available by the time that envelope reaches the printer in order to avoid having the envelope routed to a "reject" hand sortation bin. Since the envelopes are moving at a continuous velocity, all of the processes must be performed in real-time. This absolute real-time requirement has, in the past, resulted in relatively high "reject" rates.
In an optimally realized system design for applications such as mail bar coding, the summed segmented-process times (pipe-line time) may be quite substantial. Accordingly, in the interest of minimizing the reject rate, very long transports have been employed. For example, mail bar coding systems are known which employ a long, serpentine-like belt path between the point of document imaging, i.e., the process start point, and the bar code printer station, i.e., the process deadline point. It is to be noted that the amount of time required to complete any process step in the system may vary from item to item. The total summed pipe-line time, accordingly, is variable and can be statistically expected to sometimes achieve extreme values. Under such circumstances, the best sub-process management design scheme is typically a linear process queue with a queued buffer between successive process stages. It is well known that designs which allow longer queue lengths, length being a function of time and distance, always achieve higher performance levels by virtue of better use of available resources. However, transport design factors that mitigate against optimizing queue length for an application such as mail bar coding include:
a. longer distances occupy greater space and require more costly transport mechanics,
b. longer distances result in more items being queued, and
c. increasing the number of queued items increases the demands on item tracking and preservation of sequence fidelity as the items converge with the computer process output at the process deadline point.
Because of the factors discussed above, virtually all high-speed linear-sequential paper item transports presently used in processes which require significant pipe-line delays compromise realization of an ideally long pipe-line process time to accommodate mechanical and control realities of high-speed paper movement. In some applications, high-speed image-based check processing for example, a "two-pass" approach is implemented wherein linkage information is printed on each item during the first pass and is read on the second pass with the time lapse between successive passes allowing "off-line" completion of item information processing from image. In other applications, the processing of selected items is "aborted" when completion time requirements are exceeded. Under such circumstances, the ejected or offending items are mechanically routed to a reject bin for manual exception handling.
Another prior art approach to achieving necessary pipe-line delays has been to employ an intermediate stacker/document accumulator. This approach necessarily dictates that the transport system be provided with a secondary document feeder which extracts items from the accumulated stack. In principle, resort to use of an intermediary stack of accumulated items allows a long process delay-time. However, all document feeders, a document feeder being a device which when functioning properly both singulates and advances the paper items being processed, have two failure modes. A failure to feed or advance a document, i.e., a paper jam, is 100% detectable. However, a singulation failure, i.e., the simultaneous feeding from the stack of plural items, is not always detectable and will cause loss of linkage fidelity. Restated, two paper items stuck together at initial infeeding might separate on out-feeding or two successive items separately in-fed may out-feed together. Either event leads to the loss of linkage or registration of two queues, i.e., the mechanical or item queue and the computer process queue, which were in registration at an initial point. Once linkage fidelity is loss, all successive items are processed erroneously and the occurrence of these linkage failure errors will not be detectable by the system.